In Global Navigation Satellite Systems (GNSSs), satellite vehicles (SVs) transmit signals that are received by receivers. For each SV, both the SV and the receivers generate a same pseudo-random noise (PRN) code. The code generated for each SV is different, but they are not orthogonal to each other. Upon detecting a signal, a receiver can cross-correlate the signal with each of a set of PRN codes. Based on the results of cross-correlations, the receiver can estimate which SV transmitted the signal and a time that it took the signal to propagate from the SV to the receiver. The receiver can then use a set of these estimations, each being associated with a different signal and SV, to estimate a distance separating the receiver from each SV in the set. Based on these differences and on known locations the SVs, the receiver can estimate its location.
In many GNSSs, all SVs share the same frequency band. Depending on propagation conditions, power of the SVs at the receiver can vary greatly. In attempt to detect a signal possibly from a weak SV, the receiver may mistakenly identify leakage of the signal from a strong SV as being from a different SV. This can result in a false “detection” of a signal from the second SV, which can impair the accuracy of the position estimation.
Various “mask” techniques can be used to reduce the false detections. In these instances, it is estimated that a weak signal is attributable to cross-correlations between a strong signal and the PRN code at issue (due to the non-orthogonal nature of the signals) if one or more conditions are met. However, if the conditions are too stringent, then these techniques preclude utilization of informative signals in estimating the receiver's location. This can thereby increase the location-estimation time and/or decrease the location-estimation accuracy.
These consequences can be even further pronounced in GNSSs in which a signal is modulated not only by a PRN code but also by an overlay code. The overlay code can result in instances in which a strong SV signal could produce sizable cross-correlation values with a various PRN codes over a broad frequency domain. Thus, to avoid false SV detections, mask techniques can extend the conditions under which a SV signal is to be attributable to a strong-SV signal. This amplifies the time and accuracy impairments on location-estimation efforts.